Zinc is an essential micronutrient in human nutrition and its importance to human health was recognized relatively recently. It is naturally present or added in some foods, or else available as a dietary supplement.
Zinc is present in many enzymes which are essential for metabolism. It plays a role, in particular, in immune system, protein synthesis, wound healing or DNA synthesis. Zinc also supports normal growth and development during pregnancy, childhood and adolescence, and is required for proper sense of taste and smell.
The human body of a healthy adult contains about 2 to 3 g of zinc. Moreover, a daily intake of zinc is required to maintain a steady state because the body has no specialized zinc storage system. Intake recommendations for zinc are provided in the Dietary Reference Intakes (DRIs) which require about a 10 to 15 mg of dietary zinc per day. These values vary by age and gender.
Generally intake of zinc occurs through food and less frequently through drinking water which is not regarded as an important nutritional source of this element. Indeed, the carbonates, oxides and sulphides of zinc are sparingly soluble, and therefore zinc is present in natural waters at low concentrations.
However, zinc is generally found in small amount in a number of foods (oysters, meats, entrails, whole bread, eggs, fishes, dried vegetables), and poorly diversified feedings can lead to zinc deficiency.
In addition, the World Health Organization has revealed a certain number of countries in which some high zinc deficiencies have been observed, especially for children and pregnant women, due mainly to country-specific foods. Among them, we can mention India, Pakistan or Nigeria.
Providing zinc-containing foods or drinks wherein zinc can be absorbed in an optimal way is then to be considered in many situations and, in particular, in these countries. Furthermore, for practical and economic reasons, it is preferable to add zinc in beverages and especially in drinking water for human consumption.
However, in some zinc-containing waters having specific pH characteristics, for example pH over 7.5 to 8.5, and more particularly in still drinking waters, zinc will combine with water molecules to lead to insoluble hydroxides (i.e. Zn(OH)2). This insoluble component will lead to non-homogeneity of zinc concentration in water and to the presence of unpleasant sediment in the water.
Moreover, in commonly used plastic bottle made, for example, of polyethylene terephthalate (PET), once precipitated in insoluble zinc hydroxide, zinc will interact with the plastic walls of the bottle and will stick to the walls. It is then not possible for a person drinking said water to absorb the whole amount of zinc present in the bottle. Thus, the consumer cannot foresee the absorbed amount of zinc even after finishing the bottle.
This issue of instability of zinc in zinc-containing still drinking waters is accentuated with time. Indeed, pH usually increases during storage and thus zinc-solubility decreases.
As consumer concern grows regarding more natural and healthier food and drinks, there has been a desire to favor the use of natural and healthy means for treating drinking water. These treatments may consist in improving the taste and quality of the water and also improving shelf stability.
It is therefore an object of the invention to provide a method of improving the solubility of zinc in zinc-containing still drinking water which comprises a step of carbonating with low carbon dioxide concentration, or to at least provide a useful alternative. The resulting drinking water may remain homogeneous through its improved solubility of zinc and thus may be compatible with usual conditions and time storage and commercialization of packaged water.